Generating seismic vibrator signals

ABSTRACT

A method and apparatus for generating a seismic source signal are provided for generating energy in the form of a plurality of time sequence vibratory signals, the vibratory signals being partitioned as a function of time and/or frequency, wherein each of the plurality of signals comprises a distinguishing signature. The partitioned vibratory signals are emitted into a terrain of interest as seismic source signals for conducting a seismic survey.

BACKGROUND

1. Technical Field

The present disclosure generally relates to seismic prospecting and inparticular to methods and apparatus for acquiring and processinggeophysical information.

2. Background Information

In the oil and gas exploration industry, geophysical tools andtechniques are commonly employed in order to identify a subterraneanstructure having potential hydrocarbon deposits. Seismic vibratoryenergy sources, or simply seismic vibrators, have been used in the fieldmany years for generating source signals. A seismic vibrator in itssimplest form is merely a heavy vehicle that has the ability to shakethe ground at a predetermined range of frequencies to impart vibratoryseismic signals into the subsurface of the earth over a specified periodof time, which allows for an instantaneous energy level less thanimpulsive generators such as dynamite.

The imparted energy, termed “seismic source signals” herein, travelsthrough the subsurface and reflects some of the energy from subsurfacegeological structures or layers. The reflected energy is thentransmitted back to the earth's surface where it is recorded using anearth motion detector. The recorded data is processed and interpreted toyield information about location and physical properties of subsurfacestructures and layers.

The seismic source signal is typically a sweep signal, or simply sweep.Sweeps are sinusoidal vibrations and may have duration times on theorder of about 5 to longer than 20 seconds depending on the terrain, thesubsurface lithology, economic constraints and physical capabilities ofthe vibrator. The sinusoidal sweep can be increased in frequencyovertime, which is called an “upsweep”. The upsweep is the signal usedtypically in modern seismic exploration. Also, the sinusoidal sweep canbe decreased in frequency overtime, which is called a “downsweep”. Theend products of the vibrator sweep are waves that propagate through theearth to return information about the subsurface.

The seismic waves travel through the ground and reflect off subterraneanformations. Boundaries between formations of differing material, densityor structure often reflect seismic waves, and seismic informationrelating to these waves is collected, processed interpreted to generatea representation or “pictures” of the subsurface. Any number ofexploration systems may be used to gather the desired information forprocessing. Receiver sensors such as velocity geophones, accelerometersand/or hydrophones may be laid out in lines, or optionally towed in thecase of hydrophones, for measuring the amplitude of seismic waves due tothe seismic source, reflected off subsurface boundaries, and thenreturning to the deployed sensors. Multiple source point acquisitionsurveys provide a method of reducing the time to acquire a completesurvey area of data. Traditional single source point acquisitionacquires one source point of data at an exclusive time. Multiple sourcepoint acquisition is used to acquire many source points of data at anexclusive time, providing for faster acquisition of the data overtraditional single source methods. In order to separate each source forman acquired multiple source record, contemporary multiple source methodsemploy methods that emit longer signals or increase the number ofvibratory signals emitted in comparison to the tradition single sourceemission.

SUMMARY

The following presents a general summary of several aspects of thedisclosure in order to provide a basic understanding of at least someaspects of the disclosure. This summary is not an extensive overview ofthe disclosure. It is not intended to identify key or critical elementsof the disclosure or to delineate the scope of the claims. The followingsummary merely presents some concepts of the disclosure in a generalform as a prelude to the more detailed description that follows.

Disclosed is a method and apparatus for generating a seismic sourcesignal. In one aspect a method includes generating energy in the form ofa plurality vibratory signals being time sequence signals partitioned asa function of time, wherein each of the plurality of vibratory signalscomprises a distinguishing signature. The vibratory signals are emittedinto a terrain of interest as seismic source signals.

In another aspect, a method for geophysical information acquisitionincludes positioning a plurality of seismic receivers in a terrain ofinterest and receiving a plurality of seismic source signals with theplurality of seismic receivers, the seismic source signals being timesequence signals partitioned as a function of time and/or frequency,wherein each of the plurality of seismic source signals comprises adistinguishing signature.

In another aspect, a method for processing geophysical informationincludes receiving recorded seismic information, the recorded seismicinformation including a plurality of seismic signals, the seismicsignals being time sequence signals partitioned as a function of timeand/or frequency, wherein each of the plurality of signals comprises adistinguishing signature. The method further includes processing theseismic information to separate the seismic information with respect toeach of the plurality of signals.

An apparatus according to one aspect includes a baseplate that iscoupled to a surface of the earth, a reaction mass that is moved withrespect to the baseplate, and a feedback-controlled actuator coupled tothe reaction mass, the feedback controlled actuator providing a force tothe reaction mass that induces linear movement of the reaction mass, thelinear movement of the reaction mass causing seismic energy propagationinto the earth, wherein the seismic energy is in the form of a pluralityof time sequence seismic signals, the seismic signals being partitionedas a function of time, wherein each of the plurality of seismic signalscomprises a distinguishing signature.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed understanding of the present disclosure, reference shouldbe made to the following detailed description of the severalnon-limiting embodiments, taken in conjunction with the accompanyingdrawings, in which like elements have been given like numerals andwherein:

FIG. 1 illustrates a non-limiting example of a method for generating andpropagating seismic energy into the earth;

FIGS. 2A-2C illustrate a non-limiting example of generating a vibratorsystem input signal having a unique signature;

FIGS. 3A-3D illustrate a non-limiting example of a method for generatingunique input signals for a four-source seismic source signal generatingscheme where each input signal has a unique signature;

FIG. 4 schematically illustrates a non-limiting example of a landseismic vibrator system for generating and propagating compressionalwave energy into the earth;

FIG. 5 is another schematic illustration of a non-limiting land seismicvibrator system for generating and propagating transverse wave energyinto the earth's surface;

FIG. 6 illustrates an example of a land seismic vibrator system having adrive external to a reaction mass; and

FIG. 7 illustrates an example of a land seismic vibrator system having adrive internal to a reaction mass.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present disclosure uses terms, the meaning of which terms will aidin providing an understanding of the discussion herein. For example, theterm information processing device as used herein means any device thattransmits, receives, manipulates, converts, calculates, modulates,transposes, carries, stores or otherwise utilizes information. Inseveral non-limiting aspects of the disclosure, an informationprocessing device includes a computer that executes programmedinstructions for performing various methods.

Geophysical information as used herein means information relating to thelocation, shape, extent, depth, content, type, properties of and/ornumber of geologic bodies. Geophysical information includes, but is notnecessarily limited to marine, transition zone, ocean bottom cable andland seismic information. Seismic information as used herein includes,but is not limited to, one or more or any combination of the following,analog signals, digital signals, recorded data, data structures,database information, parameters relating to surface geology, sourcetype, source location, receiver location, receiver type, time of sourceactivation, source duration, source frequency, energy amplitude, energyphase, energy frequency, wave acceleration, wave velocity and/or wavedirection.

Geophysical information may be used for many purposes. In some cases,geophysical information such as seismic information may be used togenerate an image of subterranean structures. Imaging, as used hereinincludes any representation of a subsurface structure including, but notlimited to, graphical representations, mathematical or numericalrepresentation, strip charts or any other process output representativeof the subsurface structure.

The term “reaction mass” is used herein in conjunction with a seismicvibrator. Land seismic vibrators according to the disclosure may use aheavy weighted structure that reciprocates to impart controlled energyinto the earth. This heavy weighted structure is generically termed a“reaction mass” herein. A “reaction mass” may move relative to othervibrator structures, such as a baseplate.

Disclosed is a simultaneous or asynchronous seismic vibrator multiplesourcing apparatus and method that operates in an acquisition time framesignificantly shorter than current seismic vibrator multiple sourcingmethods. Vibration duration using the disclosed methods and apparatusare comparable to conventional seismic vibrator single source duration,while providing data separation comparable or superior to currentmultiple source techniques, by emitting a set of low distortion timesequences that are uniquely partitioned in frequency and/or phase as afunction of time such that each source within the set emits a distinctsignature. The new partitioning methods disclosed will allowapproximately the same sweep times (6-12 seconds) and sweep effort asconventional single source point acquisition. Time efficiency advantageswill be realized by the disclosed methods using single source protocolsor using multi-source protocols.

FIG. 1 illustrates a non-limiting example of a method for generatingseparable seismic source signals. In general, the method 100 includesreceiving an input signal at a seismic vibrator 102, generating energyin the form of a plurality of time sequence vibratory signals 104, andemitting the vibratory signals into a terrain of interest 106 as seismicsource signals.

The “input signals” in several non-limiting embodiments are the desiredsignal forms for a particular seismic survey. In an ideal case, theseismic source signal traveling in earth is identical to the inputsignal. The input signals may be created off site of the survey locationor the input signals may be generated at the survey location. Oncegenerated, the input signals are loaded onto the vibrator or vibratorsfor use by the vibrator electronics, e.g. the controller, to control thevibrator system. The vibrator system converts the input signals tokinetic energy in the vibrator reaction mass. The energy in the vibratorsystem reaction mass will be referred to herein ss the vibratory signal.

In several non-limiting embodiments, several seismic vibrators arepositioned on or near the terrain of interest. The individual seismicvibrators may be of any type seismic vibrator that is capable ofcontrolling distortion to a level that enables signature separationduring processing in field units or in a seismic information processingfacility. Suitable non-limiting vibrators may include a hydraulicactuator system having a feedback control circuit for controllingharmonic distortion. One example of such a vibrator is disclosed in U.S.patent application Ser. No. 11/691,925 for “Apparatus and Method forGenerating a Seismic Source Signal,” the entire specification of whichis hereby incorporated herein by reference. Other non-limiting examplesof suitable vibrators include seismic vibrators having controlled linearelectric motor actuators. Some examples of which are described below.

Variations in the allowable distortion level of generated signals may beaccommodated by separation processing methods where the emitted signalsignatures are distinct enough for recognition within the band ofdistortion. In general, the term “low distortion” as used herein relatesto total harmonic distortion (THD). THD adds risk to the ability toseparate recorded information, and the acceptable level of THD may varyand may depend on one or more factors. Some factors that may allow forhigher or lower acceptable THD include the particular seismic record,recording methods used, filtering methods used, subtraction methods usedand information processing methods. Therefore, the term “low distortion:should be considered herein as meaning an acceptable level of THD. Inmost cases, a THD of less than about 5% will be acceptable. In someembodiments, acceptable THD may be 5% or or more. Source separation inany particular seismic information acquisition operation will be afunction of the source geometry, signal strength, and uncorrectedvibrator distortion.

In several embodiments, the input signals are frequency partitioned withrespect to time in order to form input signals having distinctsignatures. In another embodiment the input signals are phasepartitioned with respect to time in order to form signals havingdistinct signatures. In other non-limiting embodiments the input signalsmay be partitioned by a combination of frequency and phase with respectto time.

Several seismic vibrators may be operated to emit respective partitionedvibratory signals as seismic source signals closely matching respectiveinput signals at the about the same time or in a substantiallysimultaneous manner. In another embodiment, the partitioned vibratorysignals may be emitted as seismic source signals in a partiallyoverlapping manner with respect to time. Alternatively, the partitionedvibratory signals may be emitted asynchronously in series.

FIGS. 2A-2C and FIGS. 3A-3C illustrate a non-limiting method ofgenerating input signals having a unique signal signature. Those skilledin the art will recognize that depicting actual signals usinggraphically unscaled data would not be practical. Thus, the figures arescaled and shifted for simplicity to illustrate the concept. FIG. 2Ashows a base signal 200 having amplitude (vertical axis) scaled to ±1.The horizontal axis illustrates 4000 data points within a sweep of 5 to25 Hz. In FIG. 2B, the base signal is segmented using a tapering processperformed by a sweep synthesizer program or other signal generatingprogram. Here, the base signal is shown segmented into four segments 202a, 202 b, 202 c and 202 d, but more or less than four segments may beused. Note that each segment has a unique frequency characteristic.Phase characteristics of several source signals will be described laterwith reference to FIGS. 3A-D. The segments of the signal 202 are thenspectrally compensated using the program to arrive at the input signalhaving unique signal signature 204.

In one non-limiting embodiment, a seismic information acquisitionoperation is performed by conducting a seismic survey using four seismicsources where each source emits a partitioned vibratory signal into theearth as a seismic source signal having a unique vibratory signalsignature closely matching the respective input signal. The seismicinformation acquired using seismic sensors may then be separatedrelative to the several source signals using information processingmethods that separate the information based in part on the signalsignatures. In the four-source example, the respective input signals maybe partitioned as shown in FIGS. 3A-3D, although other signatures arewithin the scope of the disclosure. Here, FIG. 3A shows an input signal204 having a signature as described above and shown in FIG. 2C. FIG. 3Billustrates an input signal 302 used by a second vibrator where thesecond vibrator input signal 302 has a signature unique with respect tothe signal 204 loaded in the first vibrator. Likewise, FIGS. 3C and 3Dillustrate respective unique input signals 304, 306 loaded into theelectronics of the respective vibrators and that are unique with respectto the other emitted signals 204, 302. Each unique signature inputsignal may be generated by a circulatory time shift of signals using thesegmenting and compensating process discussed above with respect to abase signal 200.

FIG. 4 schematically illustrates a non-limiting example of a landseismic vibrator system 400 for generating and propagating seismicenergy signal into the earth in the form of a time sequence seismicsource signal that is partitioned as a function of time, wherein thesignal comprises a distinguishing signature as discussed above and shownin FIGS. 2C and 3A. The seismic vibrator system 400 includes a reactionmass 404 and a support member 406 mechanically coupled to a baseplate408. The baseplate 408 maintains physical contact with the earth'ssurface 410 during operation. The seismic vibrator system 400 includesan electric power generator 414 that provides electrical power to anelectric driver 412. A driver interface 416 provides mechanical,electrical or magnetic communication between the electric driver 412 andthe reaction mass 404. The electric driver 412 in response to the inputsignal causes the reaction mass 404 to reciprocate along one or moreaxes during operation, thereby converting the input signal to kineticenergy in the reaction mass 404. The kinetic energy is in the form of avibratory signal that closely matches the input signal.

The seismic vibrator system 400 may further include a controller 424 forcontrolling the electric driver 412 and movement of the reaction mass404. Sensors 418, 420, 422 may be used to monitor operating parametersof the system 400. In one embodiment, an output signal from the sensors418, 420, 422 may be incorporated into a feedback control circuit 426for providing control of the reaction mass 404 movement and thus bettercontrol of the system 400 output energy imparted into the earth tocontrol and maintain distortion levels to an acceptable THD.

The electric power generator 414 may be any suitable system thatgenerates sufficient power for the seismic vibrator system 400. Theelectric power generator 414 may include any suitable device orcombination of devices for supplying electrical power to the seismicvibrator system 400, including, but not limited to a gasoline engine, adiesel engine, and propane or natural gas powered generators. In oneembodiment, the electric power generator 414 can be an industrial orcommercial electrical supply network. In one embodiment, the electricgenerator can be a 250 kW three phase generator driven with a 300 to 400HP power unit. In several embodiments, the electric power generator 414provides electric power to the electric driver 412.

The electric driver 412 may include any number of drive types suitablefor moving a heavy mass, such as the reaction mass 404. The electricdriver 412 converts the electrical energy supplied by the electric powergenerator 414 to mechanical or magnetic energy sufficient to reciprocatethe reaction mass 404. In one embodiment, the electric driver 412includes rotary electric motor or several rotary electric motors. In oneexample, a “squirrel-cage” type motor may be used. In one embodiment,the electric driver 412 includes a linear electric motor or severallinear electric motors. In some cases a stator is rigidly coupled to areaction mass 404 support structure and one or more armatures may berigidly attached to the reaction mass 404. In other examples, a statoris rigidly coupled to a reaction mass 404 and one or more armatures maybe rigidly attached to a support structure. In several embodiments, theelectric driver 412 may include electromagnetic devices disposed on orabout the reaction mass 404.

Continuing with the example of FIG. 4, the driver interface 416 mayinclude any number of devices or structures suitable for interfacing theelectric driver 412 to the reaction mass 404. The driver interface 416may include a gearbox for converting energy from the electric driver 412reciprocating motion in the reaction mass 404. In one embodiment, theelectric driver 412 includes a linear induction motor, and the driverinterface 416 can be an electromagnetic interface. In severalembodiments, the energy to reciprocate the reaction mass 404 can besupplied using one or more electromagnetic devices disposed internal tothe reaction mass 404. In one or more embodiments, the energy toreciprocate the reaction mass 404 can be supplied using one or moreelectromagnetic devices disposed external to the reaction mass 404.

The reaction mass 404 can be a structure fabricated from any resilientmetallic material, such as steel, steel alloys, or any suitablecomposite material. The reaction mass 404 may be formed of a monolithicmember or may include several members suitably coupled to form areaction mass 404. The weight of the reaction mass 404 and the weight ofthe baseplate 408 may be selected according to any suitable ratio. Thereaction mass 404 can be equipped with an internal cooling system,external cooling system, or any combination thereof, to maintain theelectrical or electromagnetic driver 412 at a suitable operatingtemperature ranging from about 0° C. to about 150° C. In someembodiments, the weight of the reaction mass may be selected to be aminimum of twice the weight of the baseplate 408. The reaction mass 404can weigh from about 2,000 lbs to about 15,000 lbs, about 4,000 lbs toabout 13,000 lbs, or about 6,000 lbs to about 12,000 lbs., or about15,000 lbs. to about 40,000 lbs. The support member

The reaction mass 404 according to the example of FIG. 4 can be movedalong on a vertical axis to generate the vibratory signal according tothe input signal used. Movement of the reaction mass 404 in this mannerimparts a force to the support member 406 once per cycle using thedriver 412 and driver interface 416. The support member 406 can berigidly attached to the baseplate 408 to permit transfer of the kineticenergy from the reaction mass 404 to the baseplate 408 via the supportmember 406. The support members 406 may be fabricated from any resilientmetallic material, such as steel, steel alloys, or any suitablecomposite material capable of withstanding the force imparted from thereaction mass 404 and transferring the kinetic energy from the reactionmass 404 to the baseplate 408. The support member 406 can be rigidlyaffixed to the baseplate 408 using any suitable mechanical attachmentincluding welding, bolting, pinning, or the like. In some cases,isolators such as air bags are used to isolate the baseplate 408 fromvibrations caused by vibrator truck systems and motors. In this manner,substantially all of the energy imparted to the baseplate is that of thereciprocating reaction mass 404.

The baseplate 408 can be fabricated from any resilient metallicmaterial, such as steel, steel alloys, or any suitable compositematerial capable of supporting the weight of the reaction mass 404. Inone embodiment the weight of the baseplate is approximately one-half theweight of the reaction mass 404. In one or more embodiments, the weightof the baseplate can range from about 1,000 lbs to about 8,000 lbs,about 2,000 lbs to about 6,000 lbs, or about 3,000 lbs to about 6,000lbs.

In one embodiment, the baseplate 408 can be lowered from the transporterand placed into contact with the earth's surface 410 using either ahydraulically or electrically actuated lift system. The lift system canbe configured such that the entire weight of the transporter rests uponthe baseplate 408, thereby typically providing 60,000 pounds of downforce to maintain contact between the baseplate 408 and the earth'ssurface while the seismic vibrator system 100 is in operation.Additional external weight can be added, if necessary, to ensure contactbetween the baseplate 408 and the earth's surface 410 is maintained atall times while the seismic vibrator system is in operation.

In one embodiment, one or more sensors 418, 420, 422 can be located onor in close proximity to the seismic vibrator system 400 to provide realtime monitoring of system performance. In one embodiment, the one ormore particle motion sensors 418 can include, but are not limited tosingle or multiple axis accelerometers, or geophones mounted proximatelyto the system 400 to monitor ground movement imparted to the surface ofthe earth 410 by the system 400. In one embodiment the one or moreparticle motion sensors 420 can include, but are not limited to microelectromechanical systems (MEMS) sensors, analog accelerometers withsuitable A/D conversion and/or vibration sensors mounted on the system400. In one embodiment the one or more displacement sensors 422 caninclude laser, inductive and/or other types of proximity sensors tomeasure the displacement of the reaction mass 404 relative to thebaseplate 408.

The sensors 418, 420, 422 can be used to provide signal inputs to thecontroller 424. In one embodiment the controller 424 can be used toprovide adjustments to operating variables such as stroke, acceleration,and frequency of the seismic vibrator system 400 in response systemparameters monitored using the sensors 418, 420, 422. In one embodiment,pulse width modulation can be used to adjust the current supplied to thedriver 412 to optimize system performance based upon sub-surfaceconditions. Control adjustments may be made in real time using feedbackobtained during vibrator 400 operation.

The reaction mass 404 can reciprocate during operation along a verticalaxis normal to the surface of the earth 408. A reciprocating cycle canbegin with the reaction mass in physical contact with the support member406, and the reaction mass 404 may be raised approximately 2″ to 6″ (5cm to 15 cm) above the support member 406. At the top of a stroke, thereaction mass 404 is accelerated downward using gravity, electricalenergy, mechanical energy, or any combination thereof and then up againin a reciprocating motion that imparts energy to the support member 406.The reciprocating motion transfers kinetic energy from the reaction mass404, through the support member 406 to the baseplate 408. The energyimparted to the baseplate 408 by the reaction mass 404 establishes acompressional seismic wave (“P-Wave”) which propagates into and throughthe surface of the earth 410. The time required for the reaction mass404 to travel through one complete oscillatory cycle (“cycle time”)determines the frequency of the seismic waves generated by the seismicvibrator system 400. In one or more embodiments, the cycle time for thereaction mass 404 can be varied from about 2 to about 300 cycles persecond (Hertz).

The electrical power used to reciprocate the reaction mass 404 may bebased upon the desired frequency and amplitude of the seismic wavesimparted to the earth's surface. In one illustrative example, with areaction mass of 8,000 pounds (2985 kg), a frequency of 25 hertz (i.e.25 cycles per second), a displacement of approximately 4 inches (11 cm),and 2 G of acceleration at the point where the reaction mass 404 impartsa force to the support member 406, a minimum energy input of about 270kW may be used for moving the reaction mass 404. In this illustrativeexample, the reciprocation of the reaction mass 404 will impart a seriesof seismic waves into the earth's surface 410, each containingapproximately 5,400 foot-pounds (7,000 joules) of energy.

FIG. 5 is another non-limiting example of a seismic vibrator system 500for generating and propagating seismic energy into the earth's surface.Seismic shear waves (“S-Waves”) can be introduced into the earth'ssurface using the seismic vibrator system 500 shown. Similar to FIG. 4,the seismic vibrator system 500 can include a reaction mass 504 andsupport member 506 mechanically coupled to a baseplate 508. Thebaseplate 508 maintains physical contact with the earth's surface 410during operation. The seismic vibrator system 500 includes an electricpower generator 414 that provides electrical power to the driver 412. Adriver interface 416 provides mechanical, electrical or electromagneticcommunication between the driver 412 and the reaction mass 504. Theelectric driver 412 causes the reaction mass 504 to reciprocate alongone or more axes during operation. Similar to the system depicted inFIG. 4, the seismic vibrator system 500 may further include a controller424 for controlling the electric driver 412 and movement of the reactionmass 504. Sensors 418, 420, 422 can be incorporated into a feedbackcontrol circuit providing control of the reaction mass 504 movement andthus enhanced control of the system 500 seismic output.

Similar to FIG. 4, the system depicted in FIG. 5 can include an electricgenerator 414, in one example a 250 kW, 3 phase generate driven by a 300to 400 HP power unit, for supplying electrical power to the electricdriver 412. Also similar to FIG. 4, the driver 412 can include, but arenot limited to, rotary electric motors, linear electric motors,electromagnetic devices, or any combination thereof disposed on or aboutthe reaction mass 504. The system depicted in FIG. 5 can include adriver interface 416 including but not limited to mechanical

Similar to FIG. 4, the reaction mass 504 can be fabricated from steel,steel alloys, stainless steel, stainless steel alloys or other metalliccomposites. In one embodiment, the reaction mass 504 can be fabricatedusing one or more composite materials. In one embodiment, the reactionmass 504 can be solid member. In one embodiment, the reaction mass 504can have one or more inductive or magnetic devices disposed within orabout the reaction mass 504. In one embodiment, the weight of thereaction mass 504 can be a minimum of twice the weight of the baseplate508. In one embodiment, the reaction mass 504 can weigh from about 2,000lbs to about 15,000 lbs, about 4,000 lbs to about 13,000 lbs, or about6,000 lbs to about 12,000 lbs.

In one embodiment, the reaction mass 504 can be reciprocated on ahorizontal axis (i.e. along an axis parallel to the surface of theearth), imparting a force to the opposing side of the support member 506once per cycle, thereby imparting a lateral motion to the baseplate 508.The support member 506 can be rigidly attached to the baseplate 508 topermit the transfer of kinetic energy from the reaction mass 504 to thebaseplate 508 via the support member 506. In one embodiment, the supportmember 506 can be fabricated from any resilient metallic material, suchas steel, steel alloys, or any suitable composite material capable ofwithstanding the force imparted to the reaction mass 504 andtransferring the kinetic energy from the reaction mass 504 to thebaseplate 508. The reaction mass 504 can be equipped with an internalcooling system, external cooling system, or any combination thereof, tomaintain the electrical or electromagnetic driver 512 at a suitableoperating temperature ranging from about 0° C. to about 150° C. In oneembodiment, the support member 506 can be rigidly affixed to thebaseplate 508 using any means of mechanical attachment includingwelding, bolting, pinning, or the like. In one embodiment, the supportmember 506 can be fabricated integrally with the baseplate 508.

The baseplate 508 can be fabricated from any resilient metallicmaterial, such as steel, steel alloys, or any suitable compositematerial capable of withstanding the energy transferred from thereaction mass 504. In one embodiment the weight of the baseplate 508 canbe approximately one-half the weight of the reaction mass 504. Inseveral embodiments, the weight of the baseplate 508 can range fromabout 1,000 lbs to about 8,000 lbs, about 2,000 lbs to about 6,000 lbs,or about 3,000 lbs to about 6,000 lbs.

In one embodiment, the baseplate 508 can be lowered from the transporterand placed into contact with the earth's surface 410 using either ahydraulically or electrically actuated lift system. The lift system canbe configured such that the entire weight of the transporter rests uponthe baseplate 508, thereby typically providing 60,000 pounds of downforce to maintain contact between the baseplate 408 and the earth'ssurface while the seismic vibrator system 500 is in operation.Additional external weight can be added, if necessary, to ensure contactbetween the baseplate 508 and the earth's surface 410 is maintained atall times while the seismic vibrator system is in operation.

The sensors 418, 420, 422 can be located on or in close proximity to theseismic vibrator system 500 to provide real time monitoring of systemperformance. In one embodiment, particle motion sensors 418 can include,but are not limited to single or multiple axis accelerometers,geophones, or similar devices, mounted proximately to the system 500 tomonitor ground movement imparted by the system 500. In one embodimentthe particle motion sensors 420 can include, but are not limited toaccelerometers and/or vibration sensors mounted on the system 500. Inone embodiment the displacement sensors 422 can include laser, inductiveand/or other types of proximity sensors to measure the displacement ofthe reaction mass 504.

In one embodiment, the sensors 418, 420, 422 can be used to providesignal inputs to the feedback controller 424. In one embodiment thefeedback controller is used to provide adjustments to operatingvariables such as stroke, acceleration, and frequency of the seismicvibrator system 500 in response to sub-surface conditions. In oneembodiment, pulse width modulation can be used to accurately adjust thecurrent supplied to the driver 412 to optimize system performance basedupon sub-surface conditions. Control adjustments may be made in realtime using feedback obtained during vibrator 500 operation.

The electric driver 412 can be used to reciprocate via the driverinterface 416 the reaction mass 504 on an axis parallel to the surfaceof the earth 410. In one or more embodiments, a reciprocating cycle canbegin with the reaction mass in physical contact with the support member506. The reaction mass 504 can be axially displaced approximately 2″ to6″ (5 cm to 15 cm) in a first direction along a horizontal axis bringingthe reaction mass 504 into physical contact with the support member 506.The reaction mass 504 can then be accelerated in a second direction,180° opposed to the first direction, along the identical horizontalaxis, until the reaction mass 504 once again contacts the support member506.

The force of the reaction mass 504 can be transmitted through thesupport member 506 to the baseplate 508. Since the baseplate 508contacts the earth's surface 410, the energy imparted to the baseplateestablishes a shear or S-wave which propagates through the surface ofthe earth 410. The time required for the reaction mass 504 to travelthrough one complete reciprocating cycle (“cycle time”) determines thefrequency of the S-waves generated by the seismic vibrator system 500.In one or more embodiments, the cycle time can be varied from about 2 toabout 300 cycles per second (Hertz).

FIG. 6 illustrates another non-limiting example of an illustrativeapparatus for generating geophysical information used in imaging earthsubsurface structures. In one or more embodiments, the seismic vibratorsystem 600 includes a reaction mass 604, and a support member 606mechanically connected or affixed to a baseplate 608. The baseplate 608maintains contact with the surface of the earth 410 during operation. Inone embodiment, the seismic vibrator system 600 can include a linearelectric motor 630. In one embodiment, the one or more linear electricmotors 630 can include one or more stators 634 coupled to a vibratorsupport structure and one or more armatures 632 coupled to the reactionmass 604. The positions of the stator(s) and rotor(s) may be reversed inother embodiments. In one embodiment, the seismic vibrator system 600includes sensors 418, 420, 422 in communication with a controller 424.In one embodiment, the output from the controller 424 can be used tocontrol the linear electric motor 630 thereby adjusting the seismicsource signal generated by the seismic vibrator system 600.

In one embodiment, the linear electric motor 630 may include a linearinduction motor (“LIM”) to achieve high acceleration of the reactionmass 604. A LIM type design can have an active three-phase windingforming the one or more stators 334 and one or more passive conductorplates 632 in physical connection with, and affixed to, the reactionmass 604.

In one embodiment, the linear electric motor 630 may include a linearsynchronous motor (“LSM”) capable of achieving high speed and power at alower acceleration than a comparable LIM. An LSM type design can have anactive winding forming the one or more stators 634 and an array ofalternate-pole magnets 632 in physical connection with, and affixed to,the reaction mass 604. With an LSM type design, the one or more magnets632 can be either permanent magnets or electromagnets.

As depicted in FIG. 6, the reaction mass 604 can reciprocate along avertical axis normal to the surface of the earth 410. Using the one ormore linear electric motors 630, the reaction mass 604 can be raisedapproximately 2″ to 6″ (5 cm to 15 cm) above a neutral position andaccelerated downward using either gravity, the linear electric motor, orany combination thereof and then up again in a reciprocating motion thatimparts energy to the support member 606. The reciprocating motiontransfers kinetic energy from the reaction mass 604, through the supportmember 606 to the baseplate 608. The energy imparted to the baseplate608 from the reaction mass 604 establishes a compressional seismic wave(“P-Wave”), which propagates into the surface of the earth 410. The timerequired for the reaction mass 604 to travel through one completereciprocating cycle (“cycle time”) determines the frequency of theseismic waves generated by the seismic vibrator system 600. The cycletime for the reaction mass can be varied from about 2 to about 300cycles per second (Hertz).

Sensors 418, 420, 422 can be located on or in close proximity to theseismic vibrator system 600 to provide real time monitoring of systemperformance. In one embodiment, particle motion sensors 418 placed nearthe system can include, but are not limited to single or multiple axisaccelerometers, or geophones to monitor ground movement imparted by thesystem 600. In one embodiment particle motion sensors 420 coupled to thesystem 600 can include, but are not limited to accelerometers and/orvibration sensors to measure motion of the system components. In oneembodiment the one or more particle motion sensors 420 can include, butare not limited to micro electromechanical systems (MEMS) sensors,analog accelerometers with suitable A/D conversion and/or vibrationsensors mounted on the system 600. Displacement sensors 422 can be usedto measure the displacement or position of the reaction mass 604 duringoperation and may include laser, inductive and/or other types ofproximity sensors.

In one embodiment, the sensors 418, 420, 422 can be used to providesignal inputs to the controller 424 via a feedback circuit 326. In oneembodiment the feedback controller can provide one or more outputsignals to adjust operating variables such as stroke, acceleration, andfrequency of the seismic vibrator system 600 in response to estimatedoperating parameters. In one embodiment, pulse width modulation can beused to adjust the current supplied to the driver 412 to optimize systemperformance based upon sub-surface conditions. Control adjustments maybe made in real time using feedback obtained during operation of theseismic vibrator system 600.

FIG. 7 illustrates yet another non-limiting example of an illustrativeapparatus for generating and propagating a seismic source signal intothe earth. A seismic vibrator system 700 according to this exampleincludes a reaction mass 704, and a support member 706 mechanicallyconnected or affixed to a baseplate 708. The baseplate 708 maintainscontact with the surface of the earth 410 during operation. In one ormore embodiments, the seismic vibrator system 700 can include one ormore linear electric motors 430. The linear electric motor 730 mayinclude one or more stators 734 coupled to a vibrator support structureand one or more armatures 732 in physical connection with, and affixedto, the reaction mass 704. The positions of the stators and armaturesmay be reversed in other embodiments. The seismic vibrator system 700can include one or more sensors 418, 420, 422 in communication with acontroller 424. An output from the controller 424 may be used to controlthe electric motors 430 thereby adjusting the seismic source signalgenerated by the seismic vibrator system 700.

The linear electric motors 730 may include a linear induction motor(“LIM”) or a linear synchronous motor (“LSM”). The linear electric motor730 may be disposed internal to the reaction mass 704. In oneembodiment, the one or more stators 734 can be rigidly attached to thesupport member 706 that is further coupled to the vibrator supportstructure, and the armatures 732 can be attached to the reaction mass704; thereby permitting the inductive forces between the stator 734 andthe armatures to vibrate the reaction mass 704 along a vertical axis.

The reciprocating motion of the reaction mass 704 transfers kineticenergy from the reaction mass 704 through the support member 706 (whenused) to the baseplate 708. The energy transfer establishes acompressional seismic wave (“P-Wave”) which propagates into the surfaceof the earth 410. The time required for the reaction mass 704 to travelthrough one complete cycle (“cycle time”) determines the frequency ofthe seismic waves generated by the seismic vibrator system 700. In oneor more embodiments, the cycle time for the reaction mass can be variedfrom about 2 to about 300 cycles per second (Hertz).

Sensors 418, 420, 422 can be located on or in close proximity to theseismic vibrator system 700 to provide real time monitoring of systemperformance. In one embodiment, particle motion sensors 418 can beplaced on the ground proximate the system 700 to monitor ground movementimparted by the system 700. The ground sensors 418 may include, but arenot limited to single or multiple axis accelerometers, or geophones.Other particle motion sensors 420 may be coupled to the system 700 forestimating movement of vibrator components during operation. In oneembodiment the one or more particle motion sensors 420 can include, butare not limited to micro electromechanical systems (MEMS) sensors,analog accelerometers with suitable A/D conversion and/or vibrationsensors mounted on the system 700. Position sensors 422 may be used toestimate the position of the reaction mass 704 during operation. These

In one embodiment, the sensors 418, 420, 422 can be used to providesignal inputs to the controller 424 via a feedback circuit 426. In oneembodiment the controller 424 can provide one or more output signals toadjust operating variables such as stroke, acceleration, and frequencyof the seismic vibrator system 700 in response to sub-surfaceconditions. In one embodiment, pulse width modulation can be used toadjust the current supplied to a driver, such as the driver 412discussed above and shown in FIG. 4, to optimize system performancebased upon sub-surface conditions. Control adjustments may be made inreal time using feedback obtained during operation of the seismicvibrator system 700.

In operation methods according to the disclosure include generating aplurality of seismic source signals using several land seismic vibratorspositioned on or near a terrain of interest. In reference to the severalembodiments described above and shown in FIGS. 1-7, land seismicvibrators may be transported to a seismic survey area. A baseplate foreach vibrator is then coupled to the earth's surface. In one embodiment,the transporter can be hydraulically or electrically lifted such thatthe weight of the transporter rests upon the baseplate. If necessary,additional external weight can be added to the transporter to ensuresolid contact between the baseplate and the surface of the earth at alltimes while the vibrator is in operation. Safety sensors can beinstalled on the lift mechanism to warn of failure to lower thebaseplate prior to operation or failure to raise the baseplate prior tomoving the transporter. A reaction mass is moved in a reciprocatingmanner along one or more axes using a feedback-controlled electriclinear motor or by a feedback-controlled hydraulic actuator. Kineticenergy from the reciprocating reaction mass is transferred to thebaseplate, and a seismic source signal is propagated into the earth.Reciprocating the reaction may be accomplished using a feedbackcontrolled linear induction motor or a linear synchronous motor orcontrolled hydraulic actuator as discussed above. When using electricmotor embodiments, a drive interface may be used to convey energy fromthe electric motor to the reaction mass.

The actuator or motor and the motion of the reaction mass may becontrolled using a controller to generate energy in the form of aplurality of time sequence vibratory signals, the vibratory signalsbeing partitioned as a function of time, wherein each of the pluralityof signals comprises a distinguishing signature, and operationparameters may be monitored according to several embodiments usingsensors placed in, on or around each seismic vibrator. An output signalindicative of the estimated operating parameters may be conveyed to thecontroller via a feedback circuit, and the controller may be used toadjust acceleration, velocity, force, frequency, stroke or otherparameters of the seismic vibrator in real-time during operation toreduce and control total harmonic distortion to about 5% or less THD.Pulse width modulation can be used to adjust the current flow to theseismic vibrator system in real-time to optimize system performancebased upon observed sub-surface conditions.

Other embodiments include methods for acquiring seismic information andfor processing seismic information. In one embodiment, a method forseismic information acquisition includes positioning a plurality ofseismic receivers in a terrain of interest. The receivers are used toreceive a plurality of time sequence vibratory signals that aregenerated as described above where the vibratory signals are partitionedas a function of time. Each signal includes a distinguishing signaturethat may be separated at the receiver, at a field processor or in aprocessing facility away from the terrain of interest.

In another embodiment, a method for processing seismic informationincludes receiving recorded seismic information. The recordedinformation is created by a seismic survey where a plurality of seismicvibrators generate signals as described above and which signals arereceived by seismic receivers and recorded on a recording medium. Therecorded seismic information includes the time sequence vibratorysignals generated at the vibrators and after the signals are emittedinto the earth and have reflected off subterranean formations. Thevibratory signals are partitioned as a function of time, wherein each ofthe plurality of signals comprises a distinguishing signature. Therecorded seismic information is then processed to separate the seismicinformation with respect to each of the plurality of signals.

The present disclosure is to be taken as illustrative rather than aslimiting the scope or nature of the claims below. Numerous modificationsand variations will become apparent to those skilled in the art afterstudying the disclosure, including use of equivalent functional and/orstructural substitutes for elements described herein, use of equivalentfunctional couplings for couplings described herein, and/or use ofequivalent functional actions for actions described herein. Suchinsubstantial variations are to be considered within the scope of theclaims below.

Given the above disclosure of general concepts and specific embodiments,the scope of protection is defined by the claims appended hereto. Theissued claims are not to be taken as limiting Applicant's right to claimdisclosed, but not yet literally claimed subject matter by way of one ormore further applications including those filed pursuant to the laws ofthe United States and/or international treaty.

1. A method for generating seismic source signals comprising: generatingenergy in the form of a plurality of vibratory signals, the vibratorysignals being time sequence signals partitioned as a function of time,wherein each of the plurality of vibratory signals comprises a pluralityof segments partitioned from a sweep signal, each of the segments has apartition of sweep frequencies different from the other segments, thesegments being arranged together in each of the vibratory signals, eachof the vibratory signals comprising a distinguishing signature of thesegments different from the other vibratory signals; and emitting thevibratory signals into a terrain of interest as seismic source signals.2. A method according to claim 1, wherein the signals of the pluralityof vibratory signals are frequency partitioned as a function of time. 3.A method according to claim 1, wherein the signals of the plurality ofvibratory signals are phase partitioned as a function of time.
 4. Amethod according to claim 1, wherein the plurality of vibratory signalsare emitted into the terrain of interest asynchronously.
 5. A methodaccording to claim 1, wherein the plurality of vibratory signals areemitted into the terrain of interest at least partially overlapping intime.
 6. A method according to claim 1, wherein the plurality ofvibratory signals are emitted into the terrain of interest substantiallysimultaneously.
 7. A method according to claim 1, wherein generatingenergy includes using a plurality of land seismic vibrators positionedat the terrain of interest.
 8. A method according to claim 1, whereingenerating energy includes using a land seismic vibrator that includesan electrical linear motor moving a reaction mass, the electrical linearmotor having a feedback controller for reducing distortion in theemitted energy.
 9. A method according to claim 1, wherein generatingenergy includes using a land seismic vibrator that includes a hydraulicsystem moving a reaction mass, the hydraulic system having a feedbackcontroller for reducing distortion in the emitted energy.
 10. A methodaccording to claim 1, wherein the distinguishing signatures of thevibratory signals enable the seismic source signals to be separated fromone another when received at a seismic receiver.
 11. A method forgenerating seismic source signals comprising: segmenting a base signalinto a plurality of segments partitioned as a function of time, the basesignal sweeping from an initial frequency to a final frequency, whereineach of the segments of the segmented base signal has a partition ofsweep frequencies different from the other segments; generating aplurality of vibratory signals from the segmented base signal byarranging the segments together in each of the vibratory signals, eachof the vibratory signals having a distinguishing signature of thesegments different from the other vibratory signals; and emitting energyinto a terrain of interest as seismic source signals by operating aplurality of seismic vibrators with the generated vibratory signals. 12.The method of claim 11, wherein the signals of the plurality ofvibratory signals are frequency partitioned as a function of time. 13.The method of claim 11, wherein the signals of the plurality ofvibratory signals are phase partitioned as a function of time.
 14. Themethod of claim 11, wherein the seismic vibrators are operatedasynchronously.
 15. The method of claim 11, wherein the seismicvibrators are operated at least partially overlapping in time.
 16. Themethod of claim 11, wherein the seismic vibrators are operatedsubstantially simultaneously.
 17. The method of claim 11, whereingenerating the vibratory signals from the segmented signal comprisesgenerating an arrangement of the segments at a first point in time,providing a listening time after the arrangement, and repeating the actsof generating the arrangement and providing the listening time atsubsequent points in time.
 18. The method of claim 11, whereingenerating the vibratory signals from the segmented signal comprisesgenerating an arrangement of the segments in each of the vibratorysignals that is different from the arrangement used in the othervibratory signals.
 19. The method of claim 11, wherein thedistinguishing signatures of the vibratory signals enable the seismicsource signals to be separated from one another when received at aseismic receiver.
 20. A method for generating seismic source signalscomprising: partitioning a sweep signal into a plurality of segments asa function of time, the sweep signal sweeping over a range of sweepfrequencies, each of the segments having a unique partition of the sweepfrequencies different from the other segments; generating a plurality ofvibratory signals from the partitioned sweep signal by arranging thesegments together in each of the vibratory signals, each of thevibratory signals having a unique arrangement of the segments differentfrom the other vibratory signals; and emitting energy into a terrain ofinterest as seismic source signals by operating a plurality of seismicvibrators with the generated vibratory signals.
 21. The method of claim20, wherein the signals of the plurality of vibratory signals arefrequency partitioned as a function of time.
 22. The method of claim 20,wherein the signals of the plurality of vibratory signals are phasepartitioned as a function of time.
 23. The method of claim 20, whereinthe seismic vibrators are operated asynchronously.
 24. The method ofclaim 20, wherein the seismic vibrators are operated at least partiallyoverlapping in time.
 25. The method of claim 20, wherein the seismicvibrators are operated substantially simultaneously.
 26. The method ofclaim 20, wherein the unique arrangements of the segments in thevibratory signals enable the seismic source signals to be separated fromone another when received at a seismic receiver.